Non‐invasive measurements of leaf epidermal transmittance of UV radiation using chlorophyll fluorescence: field and laboratory studies
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Ratios of chlorophyll fluorescence induced by ultraviolet (UV) and bluegreen (BG) radiation [F(UV)/F(BG)] were determined with a Xe‐PAM fluorometer to test the utility of this technique as a means of non‐intrusively assessing changes in the pigmentation and optical properties of leaves exposed to varying UV exposures under laboratory and field conditions. For plants of Vicia faba and Brassica campestris , grown under controlled‐environmental conditions, F(UV‐B)/F(BG) was negatively correlated with whole‐leaf UV‐B‐absorbing pigment concentrations. Fluorescence ratios of V. faba were similar to, and positively correlated with (r 2 =0.77 [UV‐B]; 0.85 [UV‐A]), direct measurements of epidermal transmittance made with an integrating sphere. Leaves of 2 of 4 cultivars of field‐grown Glycine max exposed to near‐ambient solar UV‐B at a mid‐latitude site (Buenos Aires, Argentina, 34° S) showed significantly lower abaxial F(UV‐B)/F(BG) values (i.e., lower UV‐B epidermal transmittance) than those exposed to attenuated UV‐B, but solar UV‐B reduction had a minimal effect on F(UV‐B)/F(BG) in plants growing at a high‐latitude site (Tierra del Fuego, Argentina, 55° S). Similarly, the exotic Taraxacum officinale did not show significant changes in F(UV‐B)/F(BG) when exposed to very high supplemental UV‐B (biologically effective UV‐B=14–15 kJ m −2 day −1 ) in the field in Tierra del Fuego, whereas a native species, Gunnera magellanica , showed significant increases in F(UV‐B)/F(BG) relative to those receiving ambient UV‐B. These anomalous fluorescence changes were associated with increases in BG‐absorbing pigments (anthocyanins), but not UV‐B‐absorbing pigments. These results indicate that non‐invasive estimates of epidermal transmittance of UV radiation using chlorophyll fluorescence can detect changes in pigmentation and leaf optical properties induced by UV‐B radiation under both field and laboratory conditions. However, this technique may be of limited utility in cold environments where UV and low temperatures can stimulate the production of BG‐absorbing pigments that interfere with these indirect measurements of UV‐transmittance.Keywords:
Ultraviolet
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A portable, two-wavelength fluorometer based on recording chlorophyll fluorescence induction of agronomic plants is proposed. The effects of various fertilizers on fluorescence of soybean and rapeseed were studied. It was shown that the most effective fertilizer combinations were N 15 P 15 K 15 for soybean and N 75 P 60 K 75 for rapeseed. The effects of high-intensity solar radiation on chlorophyll fluorescence of bush bean can be explained by the process qE-quenching which depends on the presence of a proton gradient across the thylakoid membrane, and qI-quenching which occurs with excessive radiation; this type of quenching provokes photoinhibition. It is possible to suggest an effect of protein structural change in chlorophyll fluorescence quenching. Ultraviolet (especially UV-B) radiation predominantly damages DNA. The main molecular alteration in UV-B-irradiated DNA is the formation of dimer photoproducts - pyrimidine dimers of cyclobutane structure which are responsible for disrupting the genetic code and damaging the photosynthetic apparatus of bush bean. In detached leaves the water deficit develops faster and therefore it is accompanied with a decline of the fluorescence indices. The proposed portable fluorometer is characterised by compactness, an independent power supply, high sensitivity, and gives a non-destructive estimate of in vivo fluorescence parameters of agronomic plants.
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The capability of laser-induced chlorophyll fluorescence (LIF) and pulse-amplitude-modulated (PAM) fluorescence technique as well as RED/NIR-light reflection measurements for detection and quantification of UV-B induced damages was evaluated in greenhouse experiments with apple seedlings ( Malus domestica Borkh.). Photosynthetic recovery from short-term UV-B stress was assessed during 7 days after UV-B treatment with the PAM fluorometer. The exposure of apple leaves to UV-B doses in the range of 10-26 W m -2 for 180 minutes (UV-B BE dose = 5.4-14 kJ m -2 ) affected neither chlorophyll content nor leaf reflection. Although UV-B damage was not visually evident 2 hours after irradiation, it could be detected by PAM and LIF fluorescence techniques with equivalent success. The intensity of LIF, estimated as the integral of fluorescence spectrum, was reduced after UV-B irradiation by 19-30%. A stronger decrease in F686 compared to F740 fluorescence resulted in significantly lower F686/F740 values in all UV-B treatments. Apple leaves displayed a strong and significant reduction in maximum fluorescence (Fm) and a slightly increase in ground fluorescence (Fo) 2 hours after UV-B treatment, as documented by PAM fluorescence measurement. Negative linear regressions between investigated UV-B doses and selected PAM parameters were found with determination coefficients (R 2 ) of 0.50 for Fv, 0.48 for Fv/Fm, and 0.58 for Fv/Fo. Among the PAM and LIF parameters tested, the Fv/Fo ratio appeared most sensitive for detection of UV-B induced damages displaying greatest changes and strongest correlation with the applied UV-B doses. PAM fluorescence images of apple leaves visualised an enhanced spatial heterogeneity of photosynthetic activity with increasing UV-B dose. The disturbance in photosynthetic functionality was followed by a continuous recovery process as indicated by restoring Fo and Fm parameters. A decline in maximum photochemical efficiency Fv/Fm from 0.80 to 0.72 and 0.43 after exposure to 20 W m -2 for 240 and 360 minutes (UV-B BE = 14.4 and 21.6 kJ m -2 ), respectively, was followed by recovery at 7 x 10 -4 and 5 x 10 -3 units per hour during the first 48 hours after UV-B treatment. The recovery curves of Fm, Fv, Fv/Fm and Fv/Fo parameters during a week after UV-B irradiation were well fitted with exponential rise to maximum function, such as: y = yo + a (1 - e-bx). However, within 7 days after exposure to UV-B light, apple leaves displayed 14% or 4% lower Fm, and 5% or 1% lower Fv/Fm values compared with control plants, indicating only a partial recovery from photoinhibition and irreversible damages in PSII.
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Plant Physiology
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The changes in PSII performance of the photosynthetic apparatus caused by environmental stress or senescence have been explored widely by applying the chlorophyll fluorescence technique, mainly by using the modulated fluorometer. In recent years, an alternative approach via analyzing chlorophyll a fluorescence transient using the continuous excitation fluorometer has been developed, which offers more information that cannot be obtained by the modulated fluorometry. The JIP-test based on the theory of energy fluxes in biomembranes has been widely used to analyze the chlorophyll a fluorescence kinetics transient helping researchers to have a deeper insight into the primary photochemical reaction in the photosynthetic apparatus. In this paper, the chlorophyll a fluorescence transient and its significance, the parameters involved and their significance in the JIP-test, and the application of the fast chlorophyll fluorescence induction dynamics analysis in photosynthesis study are introduced combining some results of the author's.
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The effects of drought stress on the chlorophyll fluorescence induction kinetics of rice varieties were studied by using PFM102 chlorophyll fluorometer. The results showed that chlorophyll fluorescence parameters including F0, Fv/F0, Fv/Fm, and T1/2 decreased in response to drought stress; there were obvious differences on change of chlorophyll fluorescence parameters among different genotypes; the chlorophyll fluorescence parameters were closely related each other. It was concluded that the change of photosynthetic the characteristics, i.e. the chlorophyll fluorescence parameters of F0, Fv/F0, Fv/Fm and T1/2, was the adaptation effect of rice to drought stress.
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A procedure is described for the rapid analysis of leaf samples to determine triazine resistance. The technique uses a commercially available fluorometer and is based upon the fact that photosynthesis-inhibiting herbicides increase chlorophyll fluorescence (because of dissipation of absorbed radiant energy in the absence of useful photochemistry). Resistant and susceptible biotypes of six weed species were assayed. Fluorescence of susceptible leaf sections increased dramatically over a 1- to 3-h exposure to atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)- s -triazine], but resistant leaf sections showed no fluorescence increase. Substantial fluorescence increases of both resistant and susceptible leaf sections were induced by diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea]. In the absence of herbicides, fluorescence was higher in resistant than in susceptible leaf sections, suggesting that the resistant biotypes are less efficient photosynthetically. Fluorescence analysis was used to characterize atrazine inhibition of photosynthesis in leaf sections of three crop species. Differences in atrazine-induced fluorescence between crop lines were relatively small and were not well correlated with atrazine tolerance. The fluorometer is a convenient device for monitoring photosynthesis inhibition, however, and could be useful in detecting plants having resistance to photosynthesis-inhibiting herbicides.
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Triazine
Photosynthetic efficiency
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This contribution is a practical guide to the measurement of the different chlorophyll (Chl) fluorescence parameters and gives examples of their development under high-irradiance stress. From the Chl fluorescence induction kinetics upon irradiation of dark-adapted leaves, measured with the PAM fluorometer, various Chl fluorescence parameters, ratios, and quenching coefficients can be determined, which provide information on the functionality of the photosystem 2 (PS2) and the photosynthetic apparatus. These are the parameters Fv, Fm, F0, Fm', Fv', NF, and ΔF, the Chl fluorescence ratios Fv/Fm, Fv/F0, ΔF/Fm', as well as the photochemical (qP) and non-photochemical quenching coefficients (qN, qCN, and NPQ). qN consists of three components (qN = qE + qT + qI), the contribution of which can be determined via Chl fluorescence relaxation kinetics measured in the dark period after the induction kinetics. The above Chl fluorescence parameters and ratios, many of which are measured in the dark-adapted state of leaves, primarily provide information on the functionality of PS2. In fully developed green and dark-green leaves these Chl fluorescence parameters, measured at the upper adaxial leaf side, only reflect the Chl fluorescence of a small portion of the leaf chloroplasts of the green palisade parenchyma cells at the upper outer leaf half. Thus, PAM fluorometer measurements have to be performed at both leaf sides to obtain information on all chloroplasts of the whole leaf. Combined high irradiance (HI) and heat stress, applied at the upper leaf side, strongly reduced the quantum yield of the photochemical energy conversion at the upper leaf half to nearly zero, whereas the Chl fluorescence signals measured at the lower leaf side were not or only little affected. During this HL-stress treatment, qN, qCN, and NPQ increased in both leaf sides, but to a much higher extent at the lower compared to the upper leaf side. qN was the best indicator for non-photochemical quenching even during a stronger HL-stress, whereas qCN and NPQ decreased with progressive stress even though non-photochemical quenching still continued. It is strongly recommended to determine, in addition to the classical fluorescence parameters, via the PAM fluorometer also the Chl fluorescence decrease ratio RFd (Fd/Fs), which, when measured at saturation irradiance is directly correlated to the net CO2 assimilation rate (PN) of leaves. This RFd-ratio can be determined from the Chl fluorescence induction kinetics measured with the PAM fluorometer using continuous saturating light (cSL) during 4-5 min. As the RFd-values are fast measurable indicators correlating with the photosynthetic activity of whole leaves, they should always be determined via the PAM fluorometer parallel to the other Chl fluorescence coefficients and ratios.
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Effect of water stress on the chlorophyll a fluorescence parameters of flag leaf of the wheat was studied with measuring result by OS30 chlorophyll fluorometer.The result indicated that the chlorophyll a fluorescence parameters of flag leaf were changed obviously under water stress.The decrease of the time from the point Fo to the point of 1/2 Fv(T1/2),the ratio of the variable to maximal fluorescence (Fv/Fm),the ratio of the variable to minimal fluorescence (Fv/Fo),variable fluorescence quenching rate(ΔFv/Fo)and Rfd(ΔFv/Ft)values under water stress suggested the primary light energy conversion of PSⅡ,the potential activities of PSⅡ,the potential photosynthetic activities and photosynthetic electron transport had been inhibited.Meanwhile effect of grouting rate of water stress was discussed.
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Water Stress
Flag (linear algebra)
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